Available since: 3.2.0
Time complexity: O(log(N))
Return the distance between two members in the geospatial index represented by the sorted set.
Given a sorted set representing a geospatial index, populated using the
GEOADD command, the command returns the distance between the two specified members in the specified unit.
If one or both the members are missing, the command returns NULL.
The unit must be one of the following, and defaults to meters:
The distance is computed assuming that the Earth is a perfect sphere, so errors up to 0.5% are possible in edge cases.
Bulk string reply, specifically:
The command returns the distance as a double (represented as a string) in the specified unit, or NULL if one or both the elements are missing.